Microsoft today issued the release-to-manufacturing (RTM) version of Windows 8.1 Enterprise Edition to its TechNet and MSDN subscribers.

This release catches up with RTM releases of Windows 8.1 and Windows 8.1 Pro that were made available to subscribers last week. Microsoft said back then that it planned to release the Enterprise edition later this month.

The RTM is the feature-complete "gold" version of the Windows 8.1 Enterprise edition, but Microsoft just recommends its use on test systems. There's no upgrade path from the RTM to finished product.

The final versions of Microsoft's Windows 8.1 operating systems, including Windows Server 2012 R2, will be available on Oct. 18, which is the "general availability" date for those products. Microsoft is promising that its deployment tools, such as "the Assessment and Deployment Kit for Windows 8.1, Microsoft Deployment Toolkit 2013, and System Center 2012 R2 Configuration Manager," will be available as well at the Oct. 18 general availability date.

Microsoft's announcement of the Windows 8.1 Enterprise edition RTM included a note at the end that may be of interest to organizations that use Microsoft's Software Assurance (SA) licensing coverage. Typically, organizations with SA coverage get access to the next version of Microsoft's software if their SA contract extends past the general availability date. However, a note from Microsoft's Erwin Visser offered something of an exception -- but only for Windows 8 Pro volume licensing (VL) users with SA coverage expiring before Oct. 18. Here's how Visser described Microsoft's offer:

To make sure that our Volume License customers running Windows 8 can experience the great benefits Windows 8.1 has to offer, organizations that acquired Windows 8 Pro through a VL agreement are licensed for Windows 8.1 Pro even if their SA expired prior to the GA release of Windows 8.1 Pro. This does not apply to Windows 8 Enterprise; you must have active SA for the Windows desktop operating system to have rights to Windows 8.1 Enterprise licenses. Windows 8.1 for production use (Pro and Enterprise) will be available through the VLSC on October 18 and for new customers to purchase through Microsoft Volume License Resellers beginning November 1.

That's good news for the organizations affected, but it seems to fly in the face of Microsoft's general licensing concepts. Microsoft hasn't explained how its more rapid release cycle will affect product licensing. As for product lifecycle considerations, Windows 8.1 is considered to be an operating system update, but it's treated as if it were a service pack release, so organizations have two years to move from Windows 8 and stay supported.

Windows 8.1 Enterprise edition comes with features that might be used by larger organizations, such as AppLocker, BranchCache, DirectAccess and virtual desktop infrastructure support, which also require using Windows Server 2008 R2 or Windows Server 2012. The Enterprise edition also offers no-cost application "sideloading," which is Microsoft's term for a way to load apps to a device from a Web portal, rather than from the Windows Store. Use of the Enterprise edition's sideloading capability also depends on having SA licensing in place. Otherwise, organizations have to buy "sideloading keys" from Microsoft.

Microsoft is also touting the security of Windows 8.1, with biometrics, multifactor authentication, encryption and improvements to Windows Defender, among others. Microsoft is backing the use of the Trusted Platform Module 2.0, which is a chip that encrypts keys used for authentication. A Microsoft blog post stated that Microsoft is "working towards requiring TPM 2.0 on all devices by January 2015." The U.S. National Security Agency last week indicated that it plans to recommend TPM for government use, although that agency has had some recent credibility issues. Meanwhile, the German government is not recommending use of TPM 2.0 at this point with Windows 8, citing loss of IT control.

For organizations trying to make sense of the differences between Windows 8.1 Enterprise edition, Windows 8.1 Pro and Window 8.1, Microsoft has published this page, showing a breakdown of features.